The evolution of reproductive endocrinology as a field in the United States and Britain will be analysed for its changing theories and experimental base in different disciplines. Anatomy, histology, medical theory and practice, embryology, genetics and biochemistry all made their contributions. My hypothesis at present is the crucial importance of physiological reasoning in the developments of this period, backed by an operational mechanism best articulated by E.H. Starling. The changing institutional context of endocrinology as a science and as a branch of medicine, and its interaction with the changing social norms of sexuality and sex roles from 1890 to 1930 will also be analysed. The materials for this analysis will be interviews with the scientific and lay participants in this field as well as library and archival materials. I will try to develop a general questionnaire that will measure the consensus of opinion of surviving scientists about the early history.